Question

I found this tutorial in A Byte of Python, but do not understand it:

import os
import time

source = [r'C:\Users\Desktop\Stuff']

target_dir = 'C:\Users\Backup'

target = target_dir + time.strftime('%Y%m%d%H%M%S') + '.zip'

zip_command = 'zip -qr "%s" %s' % (target, ' '.join(source))

if os.system(zip_command) == 0:
    print 'Successful backup to', target
else:
    print 'Backup failed!'

After checking help(os) I do not understand why os.system(zip_command) would ever be zero. .system() does not return a Boolean, does it?

thanks.

Answer 1

help(os.system) says:

system(...)
    system(command) -> exit_status

    Execute the command (a string) in a subshell.

So, it executes the command you pass as a parameter and returns the exit_status of that command.

When a program returns 0 as result, it means it was executed succesfully and if it returns anything else, it probably means there was an error somewhere.

So in this line:

if os.system(zip_command) == 0:

you are actually asking: if the command line was executed succesfully then … else …